Removed the deprecated Beautiful Soup 3 treebuilder.
beautifulsoup4 can use html5lib as a parser instead. Note that
since it doesn’t support namespaces, foreign content like SVG and
MathML is parsed incorrectly.

Removed simpletree from the package. The default tree builder is
now etree (using the xml.etree.cElementTree implementation if
available, and xml.etree.ElementTree otherwise).

Removed the XHTMLSerializer as it never actually guaranteed its
output was well-formed XML, and hence provided little of use.

Removed default DOM treebuilder, so html5lib.treebuilders.dom is no
longer supported. html5lib.treebuilders.getTreeBuilder("dom") will
return the default DOM treebuilder, which uses xml.dom.minidom.

Optional heuristic character encoding detection now based on
charade for Python 2.6 - 3.3 compatibility.